In recent years, various input devices such as a keyboard, a mouse, a joystick, and a digitizer have been used to construct interfaces between users and home appliances or information telecommunication devices. However, when the user makes use of these input devices, user's dissatisfaction increases because the user is required to know how to use the input devices and the input devices occupy space. Therefore, a convenient and simple input device that can reduce erroneous operation is required. In response to this demand, a touch sensor for enabling the user to input information by approaching or directly touching the screen with his or her hand or a pen has been suggested.
The touch sensor has a simple configuration capable of reducing erroneous operations. The user can also perform an input action without using a separate input device, and can quickly and easily manipulate a device through contents displayed on the screen. Accordingly, the touch sensor has been applied to various display devices.
The touch sensor used in the display devices may be classified into an add-on type touch sensor and an on-cell type touch sensor depending on construction thereof. The add-on type touch sensor is configured such that the display device and the add-on type touch sensor are individually manufactured and then the add-on type touch sensor is attached to an upper substrate of the display device. The on-cell type touch sensor is configured such that components constituting the on-cell type touch sensor are directly formed on the surface of the upper substrate of the display device.
There is a problem that a thickness of the display device increases because the add-on type touch sensor has the structure in which the add-on type touch sensor is mounted on the display device. Further, the visibility of the display device is reduced because of a reduction in brightness of the display device due to the increased thickness.
On the other hand, the on-cell type touch sensor shares the glass substrate with the display device because the on-cell type touch sensor has the structure in which the on-cell type touch sensor is formed on the surface of the upper substrate of the display device. Therefore, a thickness of the display device using the on-cell type touch sensor is less than a thickness of the display device using the add-on type touch sensor. However, the entire thickness of the display device using the on-cell type touch sensor increases because of a touch driving electrode layer, a touch sensing electrode layer, and an insulating layer for insulating the touch driving electrode layer and the touch sensing electrode layer which constitute the on-cell type touch sensor.
Integrated type (or in-cell type) touch sensors can solve the problems generated in the add-on type touch sensor and the on-cell type touch sensor because of the advantages of the thin profile and the durability improvement. A mutual capacitive type touch sensor among the integrated type (or in-cell type) touch sensors is configured to such that X-axis electrode lines (for example, driving electrode lines) and Y-axis electrode lines (for example, sensing electrode lines) cross over each other in a touch electrode formation area of a touch sensing panel to form a matrix, a driving pulse is applied to the X-axis electrode lines, and changes in voltages generated in sensing nodes defined as crossings of the X-axis electrode lines and the Y-axis electrode lines are sensed through the Y-axis electrode lines, thereby deciding whether or not a touch operation is performed.
In the mutual capacitive touch sensor, a mutual capacitance generated in touch recognition of the mutual capacitive touch sensor is very small, but a parasitic capacitance between gate line and data lines constituting the display device is very large. Therefore, it is difficult to accurately recognize a touch position because of the parasitic capacitance.
Further, because a plurality of touch driving lines for a touch drive and a plurality of touch sensing lines for a touch sensing have to be formed on the common electrode for multi-touch recognition of the mutual capacitive touch sensor, the mutual capacitive touch sensor requires a very complex line structure.